Refiners having flat refining surfaces generally comprise two refining discs, which rotate relative to each other and which have opposed refining surfaces. In this manner, one refining disc can be rotatable and the other stationary, or both refining discs can be rotatable in opposite directions. The refining surfaces generally consist of refining elements located on each refining disc. These refining elements are provided with a pattern of bars and intermediate grooves. Between the opposed refining elements a refiner gap is formed, through which the material is intended to pass outwardly while simultaneously being worked by the bars of the refining elements.
Refiners with conical refining surfaces comprise a rotor with a conical refining surface which is surrounded by a stator with an opposed conical refining surface. The angle of inclination to the rotor axis is generally less than 45.degree., preferably 10-30.degree.. The refining surfaces consist of refining elements located on the rotor and stator, respectively. These refining elements are provided with a pattern of bars and intermediate grooves. Between the opposed refining elements a refiner gap is formed, through which the material is intended to pass from the end with the smallest diameter to the end with the largest diameter, while simultaneously being worked by the bars of the refining elements.
The bars on the refining elements can be straight or angled, and the bar-groove ratio can be varied for achieving different refining results. The feed through the refiner gap is affected strongly by centrifugal forces. With increasing diameter in the direction of feed, the centrifugal force, and thus the feed force, also increases. The difference in diameter between the inlet and outlet of the refiner gap implies that the space for the material in the refiner gap can vary by up to 50% between the inlet and outlet portion of the refiner gap. These conditions limit the total capacity, and can cause problems with non-uniform quality of the refined material. Furthermore, there will also be a reduction in the total production due to wear of the bars on the refining elements.
One object of the present invention is to eliminate these problems by about a uniform feed through the entire refiner gap.